1. Field of the Invention
The invention relates to an intake mixture introducing apparatus which introduces gas from a common gas passage into intake air paths independently provided for each cylinder of an internal combustion engine having a plurality of cylinders, via gas introduction passages independently provided for each of the intake air paths.
2. Description of the Related Art
Exhaust gas recirculation (hereinafter simply referred to as “EGR”) is known technology for reducing oxides of nitrogen in exhaust gas of an internal combustion engine. One type of EGR is external EGR in which exhaust gas discharged from a combustion chamber is supplied to an intake system via an EGR passage (see Japanese Patent Application Publication No. 2-211369 (JP-A-2-211369) and Japanese Utility Model Application Publication No. 63-177653 (JP-U-63-177653), for example).
When performing EGR in an internal combustion engine having a plurality of cylinders, the exhaust gas concentration, i.e., the so-called EGR rate, in the intake air supplied to each combustion chamber must be adjusted so that it is the same for each cylinder in order to obtain the same combustion state in each combustion chamber. To accomplish this, the technology described in JP-A-2-211369 adjusts the amount of introduced exhaust gas so that it is the same for each cylinder by making the lengths of the flow paths from the EGR passage to the intake passage of each cylinder the same. On the other hand, the technology described in JP-U-63-177653 adjusts the amount of introduced exhaust gas so that it is the same for each cylinder by adjusting the sectional area of a distribution passage and a communicating passage according to the difference in length of the exhaust gas introduction path.
However, the lengths of the flow paths from the EGR passage to the intake passage of each cylinder may not always be able to be made the same, as they are with the structure described in JP-A-2-211369, due to limitations in the internal combustion engine. Also, the technology described in JP-U-63-177653 is limited to an internal combustion engine with four cylinders and is unable to be applied to internal combustion engine with any other number of cylinders.